In the human body a multitude of specialised cell types carry out many different functions in different organs. What they all have in common is the genome: the same set of instructions, encoded into their DNA, which regulates their abilities. So how is it possible that cells take on so many diverse jobs, shapes and populate various regions in the body that all require different specialisation? How do they decide which cell type to become – is this decision even up to them or are there external factors at play? Can cell identities and fates in fact be altered? And how would this be relevant for modern medicine?